Add network.target to unit file

Icinga2 fails with 'Cannot bind TCP socket for host',
if other services requiring network.target are not installed.

Signed-off-by: Jean Flach <jean-marcel.flach@netways.de>

fixes #10968

etc/initsystem/icinga2.service.cmake

@@ -1,6 +1,6 @@
 [Unit]
 Description=Icinga host/service/network monitoring system
-After=syslog.target postgresql.service mariadb.service carbon-cache.service
+After=syslog.target network.target postgresql.service mariadb.service carbon-cache.service
 
 [Service]
 Type=forking